Implant dentistry involves the restoration of an edentulous area in the mouth of a patient. The restorative techniques typically use artificial components, such as abutments and prosthetic teeth that are secured to a dental implant. According to state of the art techniques, this restorative process has several stages.
During an initial stage, the jawbone of the patient is exposed, and a series of drills are used to form a cylindrical cavity (the osteotomy) in the bone. A dental implant is then positioned into the cavity. In a two-stage surgical procedure, the gingival tissue is sutured, and the implant is left in the bone for several months to integrate with surrounding bone and tissue. In a single-stage procedure, this bone-integration period is skipped.
During the next stage, a mold or impression is taken to record the position and orientation of the implant within the mouth. The impression is used to create a plaster model or analogue of the implantation site. This model replicates the placement of the implant and enables dental technicians to fabricate a final prosthetic restoration. After the impression is taken, a temporary healing abutment or temporary prosthesis is attached to the implant. At this time, the gingival tissue is contoured or shaped to receive the final restoration.
In order to produce a final restoration with excellent aesthetics and functionality, the analogue must accurately reflect the position and orientation of the implant in the mouth of the patient. To help achieve this accuracy, one or more indexing means are typically provided on the proximal end of the implant and on the distal end of the impression coping. Typically, the indexing means is a hexagonal projection or indentation or other polygon formed at the coronal end of the implant. When the implant is fully installed in the jawbone of the patient, the indexing means is typically exposed through the crestal bone so that accurate mapping of the implant and surrounding jawbone can occur. However, because the indexing means of the implant is typically quite small and may be recessed partially beneath the gums of a patient, a secondary or intermediate impression element is typically used to help accurately transfer the orientation of the indexing means of the implant. This intermediate impression element is commonly called a “coping” or “impression coping.” Examples of impression copings are taught in U.S. Pat. No. 4,955,811 entitled “Non-rotational Single-Tooth Prosthodontic Restoration” to Lazzara et al.
Today, two types of impression copings are used: Transfer impression copings that use an “open-tray” technique, and pick-up impression copings that use a “closed-tray” technique. Both types are conveniently adapted to be screw-retained to the implant. The choice of which technique to use (open tray vs. closed tray) is primarily based on individual patient characteristics and preferences of the clinician.
In the closed-tray technique, a threaded screw or bolt is used to temporarily secure the impression coping to the implant fixture. Once the coping is secure, a U-shaped impression tray filled with impression material is placed in the patient's mouth over the implant site. The patient bites down on the tray and squeezes the impression material into the implantation site and area around the impression coping. Within a few minutes, the impression material cures or hardens to a flexible, resilient consistency. The impression tray is then removed from the patient's mouth to reveal an impression of the implant site and coping. The screw connecting the implant is unthreaded, and the impression coping is removed. The coping is then removed from the mouth of the patient and is transferred back into the impression material.
One advantage of the closed-tray technique is that it is simple to perform. The technique, however, is sometimes prone to inaccuracies where sufficient care is not taken during the step of reinserting the coping into the impression material.
The open-tray technique is similar to the closed-tray technique except that a pick-up coping, instead of the transfer coping, is used. The pick-up coping typically includes a portion adapted to be embedded in the impression material. This portion includes a protuberant “lip” or similar projection at the coronal aspect so the coping can be retained in the impression material. In this case, once the impression is taken and the tray is removed, the coping remains in the impression material or is “picked up” and pulled away from the mouth of the patient. To facilitate this procedure, the tray is provided with one or more apertures or openings through which a tool may be inserted to loosen the screw or bolt securing each coping. Thus, this impression technique is commonly referred to as the “open-tray” technique.
The open-tray technique is particularly well suited for multi-site dental restoration procedures, especially when a large divergence angle exists between multiple adjacent implants. The open-tray technique is generally preferred for accuracy, but it is more complex since holes or apertures may need to be cut in the tray. As a result, this technique often takes more time to prepare and execute.
It would be advantageous to have an impression coping that has advantages over prior impression copings and techniques.